When aluminium and aluminium alloys (hereinafter referred to as aluminium) are molten, dross is formed due to the oxidation of the melt and it floats up to the surface of the melt. Particularly, a great amount of dross is formed in melting the thin materials such as of can and the materials which contain in large quantity easily-oxidisable elements such as magnesium. As the demand to the similar materials increases these days, therefore, there is an increasing generation of dross when waste materials are molten.
Though the dross floated up th the surface of the melt is discharged to the outside of the melting furnace it contains a considerable amount of aluminium as metallic component. Since the amount of aluminium reaches, for example, as much as about 70% by weight, the so-called "dross recovery" is carried out in order to recover the aluminium content.
The dross constriction is such a process that the dross still at a high temperature, which has been discharged to the outside of the furnace, is exothermally stirred in a stirring apparatus, and the aluminium in the solidified or semi-solidified state is re-molten and dripped to the bottom of said apparatus thereby to be stayed there and then separated and recovered. In such a case, it is effectively carried out to add an exothermic flux in order to promote the exothermic reaction of aluminium for the re-melting.
In the dross recovery, about 30% by weight of aluminium in the dross is recovered, but usually about 40% by weight of aluminium still remains as it is dispersed in the dross. The residual aluminium repeats oxidation and heat generation when the dross is left as it is, and its metallic component is lost, and therefore the residual aluminium must be cooled quickly.
The cooling methods therefor conventionally carried out are a method of scattering the dross on the floor, a method of sprinkling water thereon, and a method of charging a cold dross thereinto.
Said cooling methods have respectively the following problems to be solved. That is, the method of scattering the dross on the floor requires a large area, so that it brings about environmental pollution due to the generation of dust. The method of sprinkling water also brings about environmental pollution due to the generation of dust and occasionally it involves danger such that the quick evaporation of water becomes explosive. On the other hand, the method of charging a cold dross has a disadvantage in that it must be charged in a considerably great amount, and it is known that this method does not render a sufficient cooling effect.